Little kids make such cute mistakes when they talk. We know they're still learning the language, so we tolerate their errors and chuckle at how funny they sound. Behind that chuckle is the assumption that the kids are getting it wrong because they just don't know the rules yet. In fact, kids' mistakes show they know a lot more about the rules than we think. The mistakes are evidence of very smart hypotheses the kids are forming from the limited data they've been given so far. Here are 10 really smart language mistakes that kids make.

1. "Dop it!" instead of "stop it!"

It's not easy to start a word with a consonant cluster. Kids don't have the fine motor control they need to produce the 'st' in stop, but they don't just leave it out. They substitute a sound they can produce. 'D' is a very smart substitution for 'st' in "stop." If you take a careful look at the acoustics of 't' in adult versions of "stop" vs. "top," you see that the 't's in those words look different from each other. The vocal cords kick in sooner for the 't' in "stop." A 'd' is basically a 't' where the vocal cords kick in sooner, so when children substitute that sound, they show they've heard the difference between "stop" and "top" and hypothesized that it's important for the language. And they are right!

2. Calls the dog "baby."

When children start using words, they haven't figured out all the situations in which they apply. They form hypotheses about word meaning and apply them on their own. The child might call all the kids and pets in the family "baby," but not the parents, revealing a hypothesis that "baby" means "family member who other people have to get food for." She may call everyone she meets "baby," extending the hypothesis to "living creatures." Like any good scientist, she can only confirm her hypothesis by testing it. Eventually, she will get enough data to settle on the right one.

3. Points to something and says "thank you" when he wants it.

This mistake shows complex knowledge of pragmatics, or the meaning of words in contexts. He knows that "thank you" is not the name of a thing in the world, but is rather something we say in a specific context. "Thank you" occurs in the context of a transfer of possession. He's saying, "Let's do that thing where 'thank you' gets said." Very clever way to try to bring about a transfer of possession!

4. "Baby drink. Milk all-gone!"

At about 18 months, children start putting two words together in phrases. But these phrases aren't just words haphazardly thrown in next to each other—they are mini sentences that express the relationships that full sentences do. "Baby drink" refers to the relation "actor performs an action." The words come in the same order they would in a grammatical sentence: subject verb. "Milk all-gone" expresses "object has some quality," and those words also come in the correct order: noun (is) adjective. The child has figured out that word order matters a lot in English for making those relations clear.

5. "I goed fast!"

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Most children go through a phase where they treat irregular verbs like they are regular. The interesting thing is that they do this after they have already learned the irregular versions. They may say "went fast" for a while, when "went" is just a word they've heard a few times. Later they notice the larger pattern—words take –ed in the past tense. Only when they've noticed that pattern, do they start making these overregularization errors. "I goed fast" is a sign that the child is not just saying words, but figuring out the larger important patterns that relate words to each other.

6. "I can't will go today."

Auxiliary verbs are hard! Can, will, do, would, should, might—there are so many little words that change the meaning of a clause. They pile up on top of each other, sometimes contracting into smaller versions, and who knows what order you're supposed to put them in? When kids pile these up, even if they don't do it correctly, they are making an amazing attempt to fit a lot of meanings together in one clause. "I can't will go today" includes information about permission status (can), negation (n't), and future tense (will) in one sentence. Trying these kinds of constructions out is a major step toward serious grammatical complexity.

7. "Ha ha. I won you."

This is not a bad guess. English has tons of verbs that can be intransitive (I watched, I pushed, I drew) or transitive (I watched you; I pushed you; I drew you.) Typically, situations where one person takes an action that affects another person will have a transitive verb associated with them. For a competitive kid of a certain age, what situation could be more stereotypically "one person affecting another" than when somebody wins?

8. "What are you eating it?"

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Questions are complicated. When you ask a question like "what are you eating," you have a situation—"you are eating it"—that you want to know something about—"you are eating what?" The child has to figure out that to ask this question in English you have to move the object of inquiry, the "what," to the beginning of the sentence, and then switch the places of "you" and "are." In "what are you eating it?" the child has correctly switched "you" and "are" and moved the "what" to the beginning. But perhaps she then felt this movement left an empty space where there shouldn't be one, and so she sticks the "it" in to fill the hole. She is making extra sure the sentence is complete.

9. "Mommy, you're a grown up. I'm a grown down."

This shows that not only has the child learned that "up" is the opposite of "down," but that that sense of oppositeness can be applied to the relationship between "adult" and "kid" in a meaningful way. Just the kind of analogy-making that came in handy when learning the difference between "good guy" and "bad guy" or "backyard" and "front yard."

10. "Unless I will get a lollipop, if I won't will get dressed fast."

So much going on here. Clausal connectors like "unless" and "if" are some of the last words that children master. In fact, when used in tests of logical reasoning, many adults have problems with them too. The child here is combining two statements: 1. Unless I get a lollipop, I won't get dressed fast. 2. I will get a lollipop if I get dressed fast. He stipulates his conditions for getting dressed fast and lays out the anticipated consequences of his getting dressed fast all in one extremely complex blend. Before we can say he's mastered English, he needs to simplify this construction down to a level that even adults can understand.